aspeed: Add Aspeed global configuration file

Create a common Aspeed layer configuration file to host pointers to
things like u-boot and kernel trees that support SOCs from Aspeed.

Tested: Built image and verified in witherspoon qemu
Change-Id: I9ad2720d8b4dff191e43be0b2c1514d25d7bf3ef
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-ast2400/conf/machine/include/ast2400.inc b/meta-ast2400/conf/machine/include/ast2400.inc
index 49c6c23..2237475 100644
--- a/meta-ast2400/conf/machine/include/ast2400.inc
+++ b/meta-ast2400/conf/machine/include/ast2400.inc
@@ -2,9 +2,7 @@
 #@NAME: Aspeed AST2400
 #@DESCRIPTION: Common machine configuration for the Aspeed AST2400 Chip
 
-PREFERRED_PROVIDER_virtual/kernel ?= "linux-obmc"
-PREFERRED_VERSION_u-boot ?= "v2016.07+git%"
-PREFERRED_VERSION_u-boot-fw-utils ?= "v2016.07+git%"
+require conf/machine/include/aspeed.inc
 
 UBOOT_MACHINE ?= "ast_g4_ncsi_config"
 UBOOT_ENTRYPOINT ?= "0x40001000"